1. Field of the Invention
The present invention relates to an ink jet system and method of use that reduces intercolor bleeding of composite color images and provides sharp black portions using two different black inks having different drying rates and definition qualities.
2. Description of Related Art
In traditional four-ink color ink jet printing (black, cyan, magenta and yellow), a major objective has been to achieve high edge definition for black-only areas, such as text, and also low intercolor bleed for color graphics. Currently, this is achieved through use of specially coated papers, thermally assisted drying of the ink or long wait times between ink passes.
Slow drying black inks generally provide high edge definition, but bleed into colors when their borders touch. Current faster drying inks have lesser bleed, but generally give lower edge definition on black text and line-art. On plain paper, there is currently no solution that gives good edge quality and eliminates intercolor bleed.
A previous attempt at reducing ink flowing between adjacent pixel areas is described in U.S. Pat. No. 4,748,453 to Lin et al., assigned to the same assignee as this invention. Lin et al. provides a checkerboard printing process that prints an alternating checkerboard pixel pattern in one pass wherein only diagonally adjacent pixel areas are deposited with ink. On a second pass the complementary checkerboard pattern is deposited to provide a complete image. Both passes are printed using the same ink.
An attempt at reducing intercolor bleed can be found in pending U.S. Ser. No. 07/927,983, assigned to the same assignee as this invention. Intercolor bleeding is reduced by examining each black pixel and a surrounding matrix of pixels of an image and determining if the pixel is bordering a color area. If so, this pixel is preferably colored using process color black (a combination of fast drying cyan, yellow and magenta inks). This reduces intercolor bleed at border areas. If the black pixels are not border pixels, that is they are part of text or in the middle of a black image, they are printed using a slow drying black ink having good picture quality because bleeding is not of a concern here.
In an optional embodiment, two differing black inks are utilized and border pixels are printed using a faster drying black ink and non-border pixels are printed using a slow drying black ink with higher picture quality.
Another attempt at reducing intercolor bleed can be found in related U.S. Ser. No. 08/176381, assigned to the same assignee as this invention. Intercolor bleed is reduced by using a slow drying black ink and fast drying CYM inks in a partial tone printing method that prints a portion of the black image and all of one of the CYM colors in a first pass and prints the remainder of the black image along with the other colors in subsequent passes.
All of these prior methods have shortcomings. While some intercolor bleed reductions are obtained, greater reductions in intercolor bleed and better edge definition are desired.